Solving Poor Settlement for Sand & Gravel Quarry

What leads to poor settlements in lagoons?

The presence of very fine and colloidal material in dirty wash water from sand & gravel washing plants often leads to poor settlement in lagoons of deep cone thickeners. Traditionally the dirty wash water from these plants is conditioned with polyelectrolyte or “floc blocks” to aid settlement but when the “fines” content is very high, traditional polymers are often unable to capture enough of these fines to sufficiently clean up the wash water before being recycled back to the wash plant.

SNF have successfully implemented alternative conditioning regimes for these “difficult” wash waters that significantly increase the solids capture resulting in clean water being returned to the wash plant. The benefits that have been realised when this dosing regime has been implemented include reduced plant down time due to unblocked nozzles on the wash plant, improved final product quality and more consolidated settled sludge which is much easier to dig out of lagoons and also makes lagoon dig out periods more predictable and easier to plan.

Dosing of the dirty wash water with the SNF range of FLOQUAT settlement aids as it leaves the wash plant at a single dose point prior to the settlement lagoons or in conjunction with traditional polyelectrolytes in deep cone thickeners has been proven to deliver significant process benefits, reduced downtime and more consistent & predictable sludge.

Dose range can vary dependent on the solids content of the dirty wash water but typically can be around 10-20ppm and the dose can be delivered using a simple digital dosing pump direct from an IBC or 25kg keg

What can SNF provide as a package to deal with the problem?

SNF will provide on-site:

Jar testing

Application survey and dosing plan

Product delivery (packaging and delivery format to suit site requirements)

Hire (or sale) of dosing pump, pipework, IBC bund

On-site technical (application) and equipment support

Collection and disposal of empty packaging

The Problem

A sand & gravel quarry in the north of Scotland was experiencing poor settlement in their lagoons which was resulting in dirty final product from the wash plant and significant downtime due to blocked nozzles in the wash plant. The slurry that was removed from the lagoons was very wet and difficult to handle when the lagoons needed to be dug out. The site had previously tried floc blocks and aluminium sulphate blocks with no success.

The Solution

SNF attended the site and carried out jar tests that identified FloQuat FL2949 as a suitable settlement aid. A suitable dosing pump was supplied and an initial dose rate of 5 litres per hour was implemented. Within 2-3 weeks, the amount of solids in the dirty wash water had been reduced to such an extent that the dose rate was able to be reduced to around 1 litre per hour. Downtime due to nozzle blockages was significantly reduced and a much more consolidated sludge that was easier to handle when the lagoons were being dug out was being produced and that the vast majority of the solids were settling out in the first lagoon.